A flail and a short length of chain on the end of a rod (think mace, not flail) can be fairly effective. It can act as a temporary entanglement weapon against spinners - my bot Scissorhands got absolutely wrecked when it sucked the end of the flail between the blade and the body. A weapon like that can also work as an overhead thwack bot to damage the lightly protected top of your opponent. Lastly the rod can be used as a keep-away device to avoid spinning weapons.

The trick is to make the rod longer than the weight + the chain so that your bot never gets tangled in its own weapon.